The present invention relates to a spark generating apparatus with a pressure sensor.
An ignition coil for an internal combustion engine that is installed directly on an engine and that is directly coupled with spark plugs is known. However, such conventional ignition coils and/or spark plugs do not generally incorporate a pressure sensor and often are large and costly to produce. A pressure sensor mounted on a spark plug is known as disclosed in U.S. Pat. No. 5,672,812 to Meyer.
Meyer discloses a magnetostrictive pressure sensor device attached to a spark plug shell. The disclosed approach, however, requires a magnetized spark plug shell. This increases cost, and subjects the resulting signal to noise due to environmental factors (e.g., magnetic and electrical noise in an automotive environment).
U.S. Pat. No. 6,119,667 to Boyer et al. disclose an integrated spark plug/ignition coil with a pressure sensor for an internal combustion engine. The sensor is disclosed as a magnetostrictive sensor, and is further disclosed as using a radially polarized biasing magnet and a sensing winding. As with the Meyer device, additional components such as a magnet are needed, which increase cost and complexity.
Additionally, piezoelectric devices have been used in a laboratory environment but are not feasible for mass production. ION sense methods of detecting cylinder pressure arc also known; however, such methods are indirect approaches for determining pressure.
There is therefore a need for an improved spark generating apparatus with pressure sensing for an internal combustion engine that minimizes or eliminates one or more problems as set forth above.
An object of the present invention is to solve one or more of the problems as set forth in the Background. An advantage of an apparatus according to the invention is that it provides a high quality signal indicative of a pressure detected in a combustion chamber of an internal combustion engine. The high quality signal is generated at a comparatively higher value than certain other pressure sensors conventionally used. Conventional pressure sensing arrangements provide reduced signal output under conditions of low cylinder pressure (i.e., idle or deceleration). The present invention provides a high signal to noise ratio under all operating conditions. Another advantage of the present invention involves flexibility of application. That is, a strain gage sensor portion of the present invention may be mounted in a variety of different locations and orientations.
An apparatus according to the present invention includes a central electrode, an insulator, a conductive shell, a second electrode, and a strain gage. The central electrode has a main axis and a first end configured for connection to a relatively high voltage source. The insulator is located outwardly of the central electrode. The central electrode further includes a second, exposed end opposite the first end. The conductive shell is located outwardly of and surrounds the insulator. The second electrode is spaced apart from the exposed end of the central electrode to define a spark gap therebetween. The second electrode is electrically connected to the shell. According to the invention, a strain gage is affixed to the shell. In operation, the shell becomes a pressure member wherein the stress applied to the shell during, for example, piston strokes, will flex the shell. The strain gage converts the deformation to a resistance change measurable by way of, for example, a bridge circuit, in one embodiment.
In an alternate embodiment, a spark generating assembly is provided that integrates an ignition coil with a spark plug configured to include a strain gage as described above. In still further embodiments, the strain gage is incorporated (i.e., applied to) into one or more fuel injectors of a Direct Gasoline Injection (DGI) engine, the glow plugs in a diesel engine, or any other component protruding into the combustion chamber. Additionally, the strain gage can be incorporated onto a cylinder head, head bolt, engine block, and/or main bearing cap or bolt. Moving parts could also be the subject of (destination for) the strain gage including the piston, connecting rod, crankshaft, and valve train components or the like.
A method of making a spark generating apparatus according to the invention is also presented.